Products made from or incorporating plastic are a part of almost any work place or home environment. Generally, the plastics that are used to create these products are formed from virgin plastic materials. That is, the plastics are produced from petroleum and are not made from existing plastic materials. Once the products have outlived their useful lives, they are generally sent to waste disposal or a recycling plant.
Recycling plastic has a variety of benefits over creating virgin plastic from petroleum. Generally, less energy is required to manufacture an article from recycled plastic materials derived from post-consumer and post-industrial waste materials and plastic scrap (collectively referred to in this specification as “waste plastic material”), than from the comparable virgin plastic. Recycling plastic materials obviates the need for disposing of the plastic materials or product. Further, less of the earth's limited resources, such as petroleum and polymers, are used to form virgin plastic materials.
When plastic materials are sent to be recycled, the feed streams rich in plastics may be separated into multiple product and by product streams. Generally, the recycling processes can be applied to a variety of plastics-rich streams derived from post-industrial and post-consumer sources. These streams may include, for example, plastics from office automation equipment (printers, computers, copiers, etc.), white goods (refrigerators, washing machines, etc.), consumer electronics (televisions, video cassette recorders, stereos, etc.), automotive shredder residue, packaging waste, household waste, building waste and industrial molding and extrusion scrap.
Different types of plastic parts are often processed into shredded plastic-rich streams. The variety of parts can vary from a single type of part from a single manufacturer up to multiple families of part types. Many variations exist, depending on at least the nature of the shredding operation. Plastics from more than one source of durable goods may be including in the mix of materials fed to a plastics recycling plant. This means that a very broad range of plastics may be included in the feed mixture.
Some of the prevalent primary polymer types in the waste plastic materials are ABS, HIPS, PP, and PC. ABS is an impact modified styrene acrylonitrile copolymer of at least one alkenylaromatic monomer, at least one of acrylonitrile and methacrylonitrile and at least one aliphatic diene or rubber. See for example, “ABS Resins”, Kirk-Othmer Encyclopedia of Chemical Technology, Third Edition, Volume 18, John Wiley & Sons, pages 442-449 (1982), for a description of ABS Resins and their method of manufacture. Suitable alkenylaromatic compounds include, for example, styrene and its analogs, such as 2-methyl styrene, chloro- and bromostyrenes, 3,5 di-methylstyrene and t-butylstyrene. The aliphatic dienes include butadiene, isoprene or chloroprene. These ABS polymers may be prepared by methods such as, emulsion, bulk and melt polymerization. A common method for preparing such polymers includes a first step of polymerizing the diene monomer or monomers to form a latex, and subsequent grafting the alkenylaromatic and nitrile monomers and any other monomers onto said latex, also while the latex is in emulsion.
HIPS is an impact modified styrene copolymer of at least one alkenylaromatic monomer and at least one aliphatic diene or rubber. See for example, “HIPS Resins”, Kirk-Othmer Encyclopedia of Chemical Technology, Third Edition, Volume 18, John Wiley & Sons, pages 442-449 (1982) for a description of HIPS Resins and their method of manufacture. Suitable alkenylaromatic compounds include, for example, styrene and its analogs, such as 2-methyl styrene, chloro- and bromostyrenes, 3,5 di-methylstyrene and t-butylstyrene. The aliphatic dienes include butadiene, isoprene or chloroprene. In addition, some HIPS copolymers may contain a small amount of acrylonitrile to improve the environmental stress crack resistance for certain applications. These HIPS polymers may be prepared by methods similar to those used to prepare ABS polymers.
PP is a homopolymer or copolymer of propylene. See for example, Dorininghaus, Plastics for Engineers, Hanser, 1988, Chapter 4, for a description of PP Resins and their method of manufacture. Homopolymer polypropylene is typically isotactic, although syndiotactic and atactic forms are also produced. Propylene copolymers include semicrystalline block copolymers of propylene with ethylene, 1-butene, or higher a-olefins, semicrystalline sequential block copolymers of propylene, ethylene and a diene or amorphous statistical copolymers of propylene, ethylene and a diene. The diene can be 1,4-hexadiene, dicyclopentadiene or 3,5-ethylidene norbomene. Copoloymers including a diene are known as EPDM. Blends of homopolymer PP with EPDM are also considered part of the PP family.
PC is a condensation polymer consisting of the carbonate functional group (—O—CO—O—) separated by aromatic groups along the polymer chain. Variations in the chemical structure of monomers or end groups may be employed to alter the properties of the PC product. See for example, Domininghaus, Plastics for Engineers, Hanser, 1988, Chapter 14, for a description of PC Resins and their method of manufacture.
Other plastics, such as styrene/acrylonitrile copolymers (SAN), polystyrene (PS), polyethylene (PE), polyamides (PA, also known as nylons), polyvinyl chloride (PVC), blends of polyphenylene ether with HIPS, PC or PA (PPO, or modified PPO), polyphenylene ethers, polyethylene terephthalate, and polybutylene terephthaltate, can also be found in waste plastic streams.
Other polymers that are used to make plastic products may also be present in the waste plastic material. Further, multiple colors and grades of ABS and HIPS, flame retardant ABS and HIPS, PP, PC, PC/ABS, polyethylene, polyesters, nylons and other plastics can be contained in the feed material to a plastics recycling plant.